Form-fill-seal machines, referred to as FFS machines, using a tubular reel of plastic material are known, and the process starts from a tubular reel for forming a bag having a given length, which bag is filled with a product and is closed or sealed once it is filled.
One of the most important work stations in this process is the fill station, in which the bag previously formed in a previous station and transferred to the fill station by conveyance means is opened at the upper part to allow the bag fill nozzle to enter the bag and discharge the product that has been prepared upstream from the bag fill nozzle through the passage formed by blades of the nozzle as they open.
In this station, the bag is filled with the metered product amount by means of using a discharge device located upstream from the bag fill nozzle, which allows reducing the total time required to perform this filling and to thereby obtain the maximum working speed of the form-fill-seal machine, since the faster the product discharge into the bag is, the lower the work cycle of this station, and accordingly, the higher the working speed, and therefore, the higher the production capacity of the form-fill-seal machine.
The device typically used to discharge the product into the bag is called a gravity discharge tube, or a gravity acceleration tube. Examples of tubes of this type are shown, for example, in patent documents ES 2,334,474 and U.S. Pat. No. 5,168,906.
One of the drawbacks of using these discharge devices, using either a system for regulation by means of a cone system or else using a system for regulating discharge by means of a discharge blade system, is that the discharge is done directly of from the weighing unit (which weighs, meters and isolates the amount of product to be used for filling the bag) onto the discharge control device in the form-fill-seal machine and in synchronicity with the placement of the empty bag in the bag fill nozzle (with an advanced positioning of the discharge to optimize the moment of arrival of the product to the bag fill nozzle).
The fact that there is a coupling at the time of product discharge between both the weighing unit and the form-fill-seal machine means that at high working speeds one of them may condition the other and therefore mutually slow one another down due to synchronism.
A solution for decoupling both systems and improving the working speed at high speeds is for the discharge device to allow decoupling both machines from one another.
An improvement to the material discharge devices existing on the market basically consists of a gravity discharge tube, the distinguishing feature of which compared to the cone or the blades controlling the product discharge is that instead of being kept in a preferably open setting adapted to the maximum flow that can be unloaded towards the fill nozzle, they have the improved feature of being completely closed when they receive the discharge from the weighing unit, not allowing any product flow downstream.
Only when the form-fill-seal machine requests that the product be discharged is this discharge gate (in the form of a cone or blades) opened to allow product discharge from the hopper. This means that as soon as the weighing unit has discharged the product in the discharge control system downstream, a metering and weighing cycle starts up again regardless of the status of the form-fill-seal machine, and in the same manner, if there were a product discharge prepared in the discharge control device, this discharge can be done at the request of the form-fill-seal machine, even if the weighing unit has not finished preparing a new metered product amount.
The gates of the product discharge device are opened and closed by means of a pneumatic-type drive, so by means of adjustment mechanisms the optimal discharge opening can be regulated so as to obtain the minimum discharge time which thus allows maximizing the working speed of the form-fill-seal machine. This solution has some drawbacks: on one hand, the use of these devices controlled by pneumatic driving means for effecting the movements of the discharge blades has a limitation in controlling the opening and closing speeds, because the sudden stops upon reaching the end positions of the drives cause vibrations and collisions (particularly when closing the blades on the discharge opening), limiting in practice the maximum working speed of this device.
On the other hand, the fact that the pneumatic control positions are fixed, or improving the fact that the position of the opening thereof is adjustable by means of mechanical regulating systems, limit the application thereof when trying to optimally adjust the device for different products, so the format change or adaptation of the open position of the discharge gates will be done by hand.
This regulation of the open position can be automated, but with a system for automatically positioning the opening stop, two basic drawbacks would remain unsolved: the limitation to the opening/closing speeds of the blades of the discharge devices, and the possibility of optimizing the discharge cycle by means of positioning the discharge blades in different positions during product discharge for the purpose of minimizing the total discharge time, for example, with a first opening for maximizing the discharge, while the outlet opening is filled with product, and a second position to finish discharging the residue when the product slides down over the actual surface of the discharge blades.
Therefore, the purpose of the present invention is to overcome the limitations existing in the current state of the art of devices which, controlled by pneumatic drives, do not allow working with high opening/closing speeds of the blades of the product discharge device in a product discharge control device with the required reliability, for example, at form-fill-seal speeds of about 2,400 to 2,750 cycles per hour.